Preferential growth orientation of laser-patterned LiNbO3 crystals in lithium niobium silicate glass

Dots and lines consisting of LiNbO₃ crystals are patterned on the surface of 1CuO-40Li₂O-32Nb₂O₅-28SiO₂ (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: λ=1064 nm), diode laser (λ=795 nm), and Yb:YVO₄ fiber laser (λ=1080 nm), and the feature of laser-patterned LiNbO₃ crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO₃ crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO₃ along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO₃ crystal lines with homogeneous surface morphologies.     

Ferroelectric Materials by the Sol-Gel Method

The sol-gel method is ideally suitable for the preparation of ferroelectric thin films such as LiNbO₃, BaTiO₃, KNbO₃ and PZT. The preparation and properties of polycrystalline, amorphous and single crystal films of these ferroelectric oxides are summarized. The origin of “amorphous ferroelectricity” is discussed. Single crystal KNbO₃ films have been successfully fabricated into planar waveguides and their ability to convert infrared laser into green light demonstrated.     

Design of heterogeneous catalysts with artificially controllable functions using effects of acoustic wave excitation

The effects of surface acoustic waves (SAWs) and resonance oscillation (RO) of bulk acoustic waves on catalytic activity and selectivity were studied in an attempt to design a heterogeneous catalyst which has artificially controllable functions for chemical reactions. The propagation of Rayleigh SAW and shear horizontal leaky SAW through thin Pd catalyst films deposited on poled ferroelectric LiNbO₃ and LiTaO₃ crystals caused considerable activity increases in ethanol oxidation: the enhancement was much larger for the oxidized than the reduced Pd. Similar effects were observed for a Ni catalyst. The RO effects on catalyst activation for ethanol oxidation were associated with the polarized (positive and negative) surfaces and the vibration modes of the ferroelectric substrates. The thickness extension mode resonance oscillation (TERO) of z-cut LiNbO3 caused different changes in the activation energy and reaction order between the positive and negative plane of the LiNbO3 substrate. Different catalyst activation was induced between TERO and the radial extension mode resonance oscillation (RERO) of a Pb_0.95Sr_0.05Zr_0.53Ti0.47O₃ ferroelectric substrate. For ethanol decomposition on a Ag catalyst, the TERO of z-cut LiNbO₃ increased ethylene production without significant enhancement of acetaldehyde production, thus demonstrating that TERO has the ability to change the selectivity in the catalytic reaction. Large dynamic lattice displacement, surface potential changes, and work function shifts were observed with TERO. A mechanism of acoustic wave excitation effect on the catalyst activation is discussed.     

Physics,chemistry and synthesis methods of nanostructured bismuth ferrite (BiFeO3) as a ferroelectro-magnetic material

Materials that combine ferroic properties, such as ferromagnetism and ferroelectricity are highly desirable, yet rare. The number of candidate materials is limited and their effects are typically too small at room temperature to be useful in applications. Bismuth ferrite (BiFeO₃) is potentially the only material which is both magnetic and highly ferroelectric at room temperature. Nanostructured BiFeO₃ are promising materials for magnetoelectric and spintronic devices, especially the memories that can be addressed both electrically and magnetically. This review paper investigates the structural, microstructural, physical concepts and different synthesis methods of BiFeO₃.     

Quantitative SIMS-analysis of erbium profiles in LiNbO3

Modern fiberoptic communication technology uses light of 1.5 μm wavelength and Er³⁺ is the laser active ion for this wavelength. Doping of crystalline LiNbO₃ (an electrooptical material) with erbium ions permits the fabrication of signal-amplifying electrooptic devices. Novel results of three different approaches have been presented to dope the near surface area of LiNbO₃ for its application in planar optoelectronics: erbium indiffusion from the surface, implantation of erbium into LiNbO₃ and subsequent annealing schemes, and the homoepitaxial growth of Er-doped LiNbO₃ on LiNbO₃ single crystalline material by a laser deposition method. These experiments are not only useful for creating integrated optical devices with active amplifying functions, but they are also important examples for fabricating and studying novel thin ferroelectric films. Secondary ion mass spectrometry (SIMS) has been employed as the main analytical tool for quantitative determination of the erbium concentration profiles.     

Composition investigation of lithium niobate crystals and its influence on the optical damage resistance

Optical methods of investigation of the defect structures and the composition of lithium niobate (LiNbO₃) single crystalsis discussed. The intrinsic defects concentrations in lithium niobate crystals (lithium vacancies (V_Li)⁻ and (Nb_Li)⁴⁺ defects, Nb on Li site in the valence state 4+), as a function of the Li/Nb ratio, are also reported. The optical damage resistance of various lithium niobate samples was investigated as a function of the composition. A remarkable increase in the optical damage resistance was found in MgO-doped almost stoichiometric lithium niobate crystals.     

Quantitative SIMS-analysis of erbium profiles in LiNbO3

Modern fiberoptic communication technology uses light of 1.5 m wavelength and Er³⁺ is the laser active ion for this wavelength. Doping of crystalline LiNbO₃ (an electrooptical material) with erbium ions permits the fabrication of signal-amplifying electrooptic devices. Novel results of three different approaches have been presented to dope the near surface area of LiNbO₃ for its application in planar optoelectronics: erbium indiffusion from the surface, implantation of erbium into LiNbO₃ and subsequent annealing schemes, and the homoepitaxial growth of Er-doped LiNbO₃ on LiNbO₃ single crystalline material by a laser deposition method. These experiments are not only useful for creating integrated optical devices with active amplifying functions, but they are also important examples for fabricating and studying novel thin ferroelectric films. Secondary ion mass spectrometry (SIMS) has been employed as the main analytical tool for quantitative determination of the erbium concentration profiles.     

铁酸铋粉体:硝酸钾辅助水热合成的形貌调控及可见光催化性能(英文)

利用硝酸钾作为辅助矿化剂,采用水热法合成了不同尺寸和形貌的铁酸铋粉体,探索了硝酸钾的加入量对产物的尺寸和形貌的影响。采用X射线衍射、扫描电镜和透射电镜以及漫反射光谱对制备的铁酸铋粉体的相结构、微观形貌以及光吸收特性进行了表征。结果显示,随着尺寸的减小,粉体的吸收带边发生蓝移。可见光降解刚果红实验表明,粒径小的铁酸铋纳米粉体颗粒具有更好的可见光催化活性。     

Super‐ and Ferroelastic Organic Semiconductors for Ultraflexible Single‐Crystal Electronics

Like silicon, single crystals of organic semiconductors are pursued to attain intrinsic charge transport properties. However, they are intolerant to mechanical deformation, impeding their application in flexible electronic devices. Such contradictory properties, namely exceptional molecular ordering and mechanical flexibility, are unified in this work. We found that bis(triisopropylsilylethynyl)pentacene (TIPS‐P) crystals can undergo mechanically induced structural transitions to exhibit superelasticity and ferroelasticity. These properties arise from cooperative and correlated molecular displacements and rotations in response to mechanical stress. By utilizing a bending‐induced ferroelastic transition of TIPS‐P, flexible single‐crystal electronic devices were obtained that can tolerate strains (?) of more than 13 % while maintaining the charge carrier mobility of unstrained crystals (μ>0.7 μ₀). Our work will pave the way for high‐performance ultraflexible single‐crystal organic electronics for sensors, memories, and robotic applications.     

LiNbO3不同晶面的光催化产氢性能

研究了LiNbO₃（001）、（100）和（110）晶面的光催化产氢性能。（001）、（100）和（110）3个晶面光催化产氢性能之比为7.8：1.3：1.0。LiNbO₃[001]晶向存在电偶极矩和自发极化,有利于增加光生电子和空穴的分离效率,减少光生电子和空穴的复合,提高LiNbO₃（001）面的光催化活性。LiNbO₃（001）面的空穴有效质量最小,有利于光生空穴的迁移,从而减少光生电子和空穴的复合,也有利于光催化性能的提高。     

Star-shaped supramolecular ionic liquid crystals based on pyridinium salts

Series of novel star-shaped liquid crystals containing [1,1?-biphenyl]-4,4?-diyl diisonicotinate mesogens with various counterions (Br^?, B-SO₃^?,C-SO₃^?,H₂PO₄^?, BF₄^?) have been synthesized and characterized, which display a nematic phase. The molecular structures of the liquid crystals, thereof consisting of rod-like mesogens linked together by different long alkyl spacers to a small disc-like core of central benzene-1,3,5-triyl triisonicotinate, have been fully characterized by ¹H NMR. Their thermal and supramolecular organization behaviours have been studied by combining polarized optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. These investigations showed that the mesophase temperature range increased with increasing alkyl chain length and the clearing point decreased with increase of anion size. These star-shaped liquid crystals have a long and ordered molecular structure, the electron delocalization of the π-π stacking conjugation effect and the electrostatic attraction of ionic make them have good ferroelectric properties and ionic conductivity properties. The interest in preparing ionic liquid crystal with a nematic phase lies in the technological applications as it is well known that the nematic phase has the highest fluidity of all liquid crystalline phases and hence the possibility to align it by applying an external electric/magnetic field, commonly used in electro-optical devices.     

Investigation of new fluxes for the single-crystal growth of stoichiometric lithium niobate

Thermoanalytical and crystal growth investigations of the ternary system Cs₂O-Li₂O-Nb₂O₅ are presented in order to grow stoichiometric LiNbO₃ (LN) crystals. Part of the phase diagram is determined and subsolidus phases are identified at room temperature by X-ray powder diffraction. Among the constituent phases, a new tetragonal cesium lithium niobate phase is assessed. From the Cs₂O-Li₂O-Nb₂O₅ system, good quality quasi-stoichiometric LN crystals can be grown.     

LiNbO_3不同晶面的光催化产氢性能

研究了LiNbO3(001)、(100)和(110)晶面的光催化产氢性能。(001)、(100)和(110)3个晶面光催化产氢性能之比为7.8∶1.3∶1.0。LiNbO3[001]晶向存在电偶极矩和自发极化,有利于增加光生电子和空穴的分离效率,减少光生电子和空穴的复合,提高LiNbO3(001)面的光催化活性。LiNbO3(001)面的空穴有效质量最小,有利于光生空穴的迁移,从而减少光生电子和空穴的复合,也有利于光催化性能的提高。     

Quantum chemistry of ferroelectric solids: Electronic structures and peculiar behavior of zero‐dimensional K3H(SO4)2‐like materials

The main problems of quantum chemistry of H‐bonded ferroelectrics are treated using the zero‐dimensional K₃H(SO₄)₂‐like crystals as suitable examples. Various quantum chemical approaches and computational procedures are applied to evaluate the Ising model coupling parameters that determine different thermodynamic and dielectric properties of these materials. The calculated Ising parameters are employed to describe the peculiarities of ferroelectric behavior of the K₃H(SO₄)₂ family crystals in the framework of mean field approximation. The problems related to the H‐bond proton (deuteron) tunneling are also discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

The structure and properties of Li1−xHxNbO3

The properties of Li_1−xH_xNbO₃ have been studied as a function of x, temperature, and stoichiometry of the LiNbO₃ used for its preparation. X-ray diffraction, thermal analysis measurements, and infrared spectroscopy have been used. The intent of this study was to gain a deeper understanding of the basic properties of this material, which has potential importance as a waveguide material in LiNbO₃ optical devices. An approximate phase diagram was constructed for the stoichiometric LiNbO₃HNbO₃ system. In one concentration range (0.56 ≤ x ≤ 0.75), particularly complex structural behavior was found: depending on x, samples undergo one, two, or three phase transitions with temperature, and the system appears to exhibit critical behavior. Samples made by proton exchange of congruent LiNbO₃ ([Li₂O]_0.486[Nb₂O₅]_0.514) show generally similar structural chemistry, with one exception: a new monoclinic phase, isomorphous with MnF₃, was found for 0.75 ≤ x ≤ 0.77. Possible reasons for the refractive index changes caused by proton exchange are discussed.     

First Principles Study of Al-Li Intermetallic Compounds

The structural properties, heats of formation, elastic properties, and electronic structures of four compositions of binary Al-Li intermetallics, Al₃Li, AlLi, Al₂Li₃, and Al₄Li₉, are ana-lyzed in detail by using density functional theory. The calculated formation heats indicate a strong chemical interaction between Al and Li for all the Al-Li intermetallics. In partic-ular, in the Li-rich Al-Li compounds, the thermodynamic stability of intermetallics linearly decreases with increasing concentration of Li. According to the computational single crystal elastic constants, all the four Al-Li intermetallic compounds considered here are mechani-cally stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill approximations, and the calculated ratios of bulk modulus to shear modulus indicate that the four compositions of binary Al-Li intermetallics are brittle materials. With the increase of Li concentration, the bulk modulus of Al-Li intermetallics decreases in a linear manner.     

Comparative investigation of LiNbO3 crystals Raman spectra in the temperature range 100–400 K

We have investigated Raman spectra of congruent and stoichiometric LiNbO₃ crystals in the temperature range 100–450 K. Slope gradient is greater for the temperature dependence of band width associated with Nb⁵⁺ ions vibrations than that associated with Li⁺ ions vibrations in a lithium niobate crystal structure. This fact indicates that the anharmonicity of Nb⁵⁺ ions vibrations along the polar axis is greater compared to Li⁺ ions vibrations. It is likely that O^2– ions contribute to this anharmonicity. The O^2– ions vibrations are characterized by an anharmonic potential in the LiNbO₃ crystal structure. The O^2– ions vibrations according to ab initio calculations strongly interact with vibrations of Nb⁵⁺ ions. We have found that the temperature dependence of the fundamental bands intensity is nonmonotonic and the “extra bands” intensity is strictly linear.     

Effect of the method used to prepare solid precursors Nb2O5:Mg on the characteristics of LiNbO3:Mg crystals produced on their basis

We investigated how the type of an extraction system affects the characteristics of precursors Nb₂O₅:Mg produced at the stage of extraction processing of niobium-containing HF-H₂SO₄ and HF-HCl solutions with an extractant comprising a mixture of dimethylamides of carboxylic acids of the C₁₀–C₁₃ fraction and 1-octanol in Escaid diluent. We also studied the optical properties of homogeneously doped crystals LiNbO₃:Mg grown from a batch synthesized with the use of pentoxide Nb₂O₅:Mg obtained from various extraction systems. On Z-cut LiNbO₃:Mg crystal wafers, such mechanical characteristics as Young’s modulus and microgravity were measured.     

Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals

Single crystals of KNbO₃ (KN), KTaO₃ (KT), and KTa_1−xNb_xO₃ (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 °C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date.     

Exploratory growth in the Li2MoO4-MoO3 system for the next crystal generation of heat-scintillation cryogenic bolometers

In this work, we report on the Czochralski growth of Li₂MoO₄ crystals up to 230 g for heat-scintillation cryogenic bolometers likely to be used in astroparticle physics and neutron spectroscopy. Their transmission properties, radiopurity levels and detector behavior characterizations were carried out in order to validate the crystal growth process. The melting characteristics, the partition coefficients of a broad range of impurities, the thermal expansion (lattice parameters and dilatometry) and specific heat properties of the crystals were measured, over a broad temperature range for the last two, providing new data likely to be used in crystal growth process numerical simulations. We also investigated the crystal growth of Li₄Mo₅O₁₇ and determined its melting behavior and specific heat. The physical properties directly relevant to heat-scintillation cryogenic bolometers of Li₂MoO₄ and Li₄Mo₅O₁₇ are discussed in the context of the current materials developed for such applications.